1. Field of the Invention:
The invention relates to a contact tip for a wire-shaped welding electrode, whose front part is designed as a contact tube and whose rear part is designed as a guide channel, the channel walls having at least one projection which constitutes an obstacle to a rectilinear feed of the electrode through the contact tip or nozzle.
Nozzles or tips of this type are used, for example, for welding torches and welding guns. The welding current is transferred in the nozzle to the wire-shaped welding electrode, which is unwound essentially, continuously, from a coil and fed through the nozzle. It is, therefore, very important that very good contact is made between the electrode wire and nozzle. In addition, it is desirable, during welding, for the position of the points in contact with the electrode in the nozzle to remain unchanged and for the welding current to always flow through an essentially uniform electrode length between nozzle and electrode tip.
However, if there is poor contact between nozzle and electrode, spark erosion occurs having an adverse effect on the life of the nozzle. The formation of sparks, on account of the relatively high voltage drop, also causes greater heating of the nozzle, which is likewise disadvantageous.
2. Background Information:
Swedish Patent Publication No. 440,617 has disclosed a contact nozzle of the generic category described above. In a section of the known nozzle, the electrode is pushed out of the rectilinear feed path by projections in the nozzle wall and thereby forced into contact with the nozzle wall at accurately defined locations.
The known nozzle is essentially tubular. There is the risk that particles dragged along by the electrode will collect at the channel restrictions caused by the projections and lead to obstructions in the nozzle which will uncontrollably slow down the feed of the electrode.
In the U.S. Pat. No. 3,112,393, a tubular contact nozzle is described with a helix-shaped passage for the electrode. Continuous electrical contact between the electrode and the inner wall of the nozzle is established throughout the length of the nozzle. The manufacture of this nozzle, which starts from a tube with small bore, is quite complicated and therefore costly.
Electrodes are often treated with a protective coating to prevent oxidation and deterioration. Moreover, the surface of the electrode may become contaminated with dust and other deleterious substances as, for example, abrased material from the electrode guides. These materials may constrict the narrow bore of a tubular contact nozzle and prohibit a uniform advancement of the electrode.